Optical tomographic imaging apparatus

Abstract

To effectively measure a tomographic image of a measurement object without changing optical path length of reference light mechanically during SS-OCT imaging.SOLUTION: An optical tomographic imaging apparatus includes a wavelength sweeping type light source, a measurement light generation part, a reference light generation part, an interference light generation part, an interference light detection part, a demultiplexer part, a data acquisition part, and an arithmetic device. The demultiplexer part converts at least one frequency of at least two interference signals. The data acquisition part digitizes an electric signal output from the demultiplexer part and acquires data. The demultiplexer part includes a down-conversion part for electrically down-converting at least one interference signal. The data acquisition part is configured to acquire data on an electric signal that has passed through at least two different routes in the demultiplexer part separately. The arithmetic device subjects the interference signal acquired in the data acquisition part to spectral analysis, and generates tomographic information on an object.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to an optical tomographic imaging apparatus. [Background technology]

[0002] Optical tomographic imaging devices that capture tomographic images of the interior of a subject's eye have been developed. For example, the optical tomographic imaging device described in Patent Document 1 includes a measurement light generation unit that irradiates the interior of the subject's eye with light from a light source and generates reflected light, and a reference light generation unit that irradiates a reference surface with light from the light source and generates reference light from the reflected light. During measurement, the reflected light (measurement light) generated by the measurement light generation unit and the reference light generated by the reference light generation unit are combined to generate interference light, which is converted into an interference signal. A tomographic image of the subject's eye is generated using the interference signal. One type of optical tomographic imaging device is called Fourier-domain optical coherence tomography (FD-OCT). There are two types of FD-OCT: spectral-domain optical coherence tomography (SD-OCT), which uses a broadband light source and a spectrometer, and swept-source optical coherence tomography (SS-OCT), which uses a wavelength-swept light source. These FD-OCT methods can capture images resolved to a desired depth of the object without changing the optical path length of the reference light during imaging.

[0003] Furthermore, in the FD-OCT method, a method has been proposed in which multiple different tomographic images are superimposed as signals at different depths. For example, Non-Patent Document 1 discloses a method in which an OCT signal of the anterior segment and an OCT signal of the fundus are superimposed as different depth signals into a single OCT signal. Non-Patent Documents 2 and 3 disclose methods in which OCT signals corresponding to different incident polarizations are superimposed as different depth signals into a single OCT signal. Non-Patent Document 4 discloses OCT signals corresponding to different light scattering angles are superimposed as different depth signals into a single OCT signal.

[0004] In optical tomography imaging devices such as those described in Patent Document 1, aliasing, a phenomenon unique to digital signal processing, occurs when interference signals exceed the Nyquist frequency, making it impossible to properly detect the depth position of the object being measured. This problem is common to FD-OCT methods. Furthermore, in Non-Patent Documents 2, 3, and 4, multiple signals are superimposed on the FD-OCT depth measurement range, reducing the effective depth measurement range to half or less compared to standard FD-OCT. This results in a problem of increased aliasing. For example, techniques for avoiding aliasing are proposed in Patent Documents 2, 3, and Non-Patent Documents 5 and 6. Patent Document 2 discloses a method for actively utilizing aliasing in SS-OCT to expand the depth measurement range. Patent Document 3 and Non-Patent Document 6 disclose a method for extracting a signal at a specific depth position by analog down-converting the SS-OCT interference signal. Non-Patent Document 5 discloses an FD-OCT with a mechanism for dynamically changing the optical path length of the reference light during imaging. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-41218 [Patent Document 2] Special Publication No. 2019-512086 [Patent Document 3] Special Publication No. 2016-503493 [Non-patent literature]

[0006] [Non-Patent Document 1] A.-H. http: / / dx.doi.org / 10.1037 / 0033-295X.101.1.13 Dhalla, D. Nankivil, T. Bustamante, A. Kuo, and JA Izatt, “Simultaneous swept source optical coherence tomography of the anterior segment and retina using coherence revival,” Opt. Lett. 37(11), 1883–1885 (2012).

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[0007] To avoid aliasing, it is necessary to detect interference signals at frequencies lower than the Nyquist frequency, even if the depth position of the object being measured changes. A simple and effective solution is to extend the depth measurement range. To do this, in SD-OCT, the number of pixels in the line scan camera used in the spectrometer must be increased, and in SS-OCT, the frequency response of the high-speed photodetector and the sampling speed of the high-speed digitizer must be improved. However, both methods increase costs, so there are limits to what can be achieved.

[0008] Another countermeasure against aliasing is to detect interference signals at frequencies lower than the Nyquist frequency by dynamically changing the optical path length of the reference light while imaging the object (e.g., Non-Patent Document 5). However, as disclosed in Non-Patent Document 5, realizing a mechanism for dynamically changing the optical path length of the reference light during imaging requires costly dynamic components such as a galvanometer scanner. Furthermore, the method disclosed in Non-Patent Document 5 makes it difficult to instantly switch or simultaneously acquire signals at different depth positions.

[0009] Furthermore, Patent Document 2 discloses a method for expanding the depth measurement range by actively utilizing aliasing in SS-OCT. However, the method disclosed in Patent Document 2 requires a specially designed wavelength scanning light source and quadrature phase modulation mechanism, which increases costs.

[0010] Furthermore, Patent Document 3 and Non-Patent Document 6 disclose a method for extracting a signal at a specific depth by analog down-converting an interference signal from SS-OCT. The methods disclosed in Patent Document 3 and Non-Patent Document 6 have the advantage that, because they are performed using analog circuits, aliasing, which is specific to digital signal processing, does not occur. However, because only signals that have become DC components through down-conversion are extracted, there is a problem in that only signals at one depth can be extracted per operation. Patent Document 3 also discloses a method for digitally down-converting an interference signal from FD-OCT to extract a signal at a specific depth. However, this method cannot adequately avoid aliasing because aliasing problems can occur when the interference signal is captured as digital data.

[0011] This specification discloses a technique that enables tomographic images of a measurement object to be effectively measured without mechanically changing the optical path length of a reference light during imaging with an SS-OCT optical tomographic imaging apparatus. [Means for solving the problem]

[0012] In a first aspect of the technology disclosed in this specification, an optical tomographic imaging apparatus includes a wavelength-swept light source, a measurement light generation unit, a reference light generation unit, an interference light generation unit, an interference light detection unit, a demultiplexer unit, a data acquisition unit, and a computing device. The measurement light generation unit irradiates an object with light from the light source and generates reflected light from the object. The reference light generation unit guides the light from the light source to generate reference light. The interference light generation unit combines the reflected light generated by the measurement light generation unit and the reference light generated by the reference light generation unit to generate at least two interference lights. The interference light detection unit outputs at least two interference signals from the at least two interference lights generated by the interference light generation unit. The demultiplexer unit converts the frequency of at least one of the at least two interference signals output from the interference light detection unit. The data acquisition unit digitizes the electrical signal output from the demultiplexer unit to acquire data. The computing device generates tomographic information of the object from the data acquired by the data acquisition unit. The demultiplexer unit includes a downconversion unit that electrically downconverts at least one of the at least two interference signals output from the interference light detection unit. The data acquisition unit is configured to separately acquire data of the electrical signals that have passed through at least two different paths in the demultiplexer unit. The calculation device performs spectral analysis of the interference signals acquired by the data acquisition unit to generate tomographic information of the object.

[0013] The above-described optical tomographic imaging apparatus electrically down-converts the interference signal in the demultiplexer unit. This makes it possible to down-convert the interference signal to within the Nyquist frequency without changing the optical path length of the reference light. This allows the required tomographic information to be acquired effectively without significantly changing the device configuration. Furthermore, the data acquisition unit is configured to separately acquire data from electrical signals that have passed through at least two different paths in the demultiplexer unit. This makes it possible to separately frequency-convert at least two interference signals and acquire data. [Brief explanation of the drawings]

[0014] [Figure 1]1 is a diagram showing a schematic configuration of an optical system of an optical tomographic imaging apparatus according to a first embodiment. [Figure 2] 4 is a diagram schematically showing the signal frequencies (or axial depth positions) of four interference signals detected by the optical tomographic imaging apparatus according to the first embodiment. FIG. [Figure 3] FIG. 2 is a block diagram showing a control system of the optical tomographic imaging apparatus according to the first embodiment. [Figure 4] FIG. 2 is a diagram showing an example of a signal processing unit included in the optical tomographic imaging apparatus according to the first embodiment. [Figure 5] FIG. 4 is a diagram showing another example of the signal processing unit included in the optical tomographic imaging apparatus according to the first embodiment. [Figure 6] FIG. 4 is a diagram showing another example of the signal processing unit included in the optical tomographic imaging apparatus according to the first embodiment. [Figure 7] FIG. 10 is a diagram showing a schematic configuration of an optical system of an optical tomographic imaging apparatus according to a second embodiment. [Figure 8] 10A and 10B are diagrams showing the signal frequencies (or axial depth positions) of four interference signals detected by an optical tomography apparatus according to Example 2, where (a) shows the interference signal detected by the first balance detector, and (b) shows the interference signal detected by the second balance detector. [Figure 9] FIG. 10 is a diagram showing an example of a signal processing unit included in the optical tomographic imaging apparatus according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] The main features of the embodiments described below are listed below. Note that the technical elements described below are independent technical elements that exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing.

[0016] In a second aspect of the technology disclosed in this specification, in the first aspect described above, the measurement light generating unit generates a first polarized measurement light that vibrates in a first direction from light of the light source, and a second polarized measurement light that vibrates in a second direction different from the first direction and has a different optical path length from the first polarized measurement light, irradiates the first polarized measurement light and the second polarized measurement light onto an object, generates a first polarized reflected light that vibrates in the first direction and a second polarized reflected light that vibrates in the second direction from the reflected light of the first polarized measurement light from the object, and generates a third polarized reflected light that vibrates in the first direction and a fourth polarized reflected light that vibrates in the second direction from the reflected light of the second polarized measurement light from the object. The interference light detection unit may detect first interference light obtained by combining the first polarized reflected light and the reference light, second interference light obtained by combining the second polarized reflected light and the reference light, third interference light obtained by combining the third polarized reflected light and the reference light, and fourth interference light obtained by combining the fourth polarized reflected light and the reference light. The down-conversion unit may down-convert an interference signal generated from the third interference light and the fourth interference light. In a polarization-sensitive optical tomographic imaging device, four interference signals having different polarization characteristics are generated. By down-converting the interference signal generated from the third interference light and the fourth interference light, it is possible to down-convert an interference signal having a frequency higher than the Nyquist frequency to a lower frequency. Therefore, in a polarization-sensitive optical tomographic imaging device, the detection sensitivity of tomographic information can be improved without changing the optical path length of the reference light.

[0017] In a third aspect of the technology disclosed in this specification, in the second aspect described above, the reference light generating unit may generate a first reference light and a second reference light having an optical path length different from that of the first reference light. The interference light detecting unit may combine the first polarized reflected light and the first reference light to detect the first interference light, combine the second polarized reflected light and the second reference light to detect the second interference light, combine the third polarized reflected light and the first reference light to detect the third interference light, and combine the fourth polarized reflected light and the second reference light to detect the fourth interference light. The down-conversion unit may down-convert an interference signal generated from the second interference light, the third interference light, and the fourth interference light. With this configuration, in the polarization-sensitive optical tomography apparatus, the interference signals can be down-converted so that the four interference signals fall within different ranges of the same frequency band.

[0018] In a fourth aspect of the technology disclosed in the present specification, in any one of the first to third aspects, at least one of the measurement light generating unit and the reference light generating unit may include a local oscillator that optically generates a signal for frequency conversion. The demultiplexer unit may down-convert the interference signal output from the interference light detecting unit using the signal generated by the local oscillator. With this configuration, the interference signal can be suitably down-converted by using the signal generated by the local oscillator.

[0019] In a fourth aspect of the technology disclosed in the present specification, in the second or third aspect described above, at least one of the measurement light generating unit and the reference light generating unit may include a local oscillator that optically generates a signal for frequency conversion. The demultiplexer unit may further include a high-pass filter. The high-pass filter may be configured to attenuate at least one interference signal having a low frequency among four interference signals generated from the first interference light, the second interference light, the third interference light, and the fourth interference light. The down-conversion unit may down-convert the interference signal that has passed through the high-pass filter using a signal generated by the local oscillator. With this configuration, only high-frequency interference signals are output to the down-conversion unit by the high-pass filter. This allows the down-conversion unit to appropriately down-convert the high-frequency interference signals.

[0020] Example 1 An optical tomographic imaging apparatus 1 according to an embodiment will be described with reference to the drawings. The optical tomographic imaging apparatus 1 of this embodiment is a polarization-sensitive OCT (PS-OCT) that is capable of capturing the polarization characteristics of a subject's eye 100 by Fourier-domain swept-source optical coherence tomography (SS-OCT) using a wavelength-swept light source.

[0021] 1, the optical tomographic imaging apparatus 1 includes a light source 11, SMFCs (single-mode fused couplers) 12, 13, and 57, a measurement light generating unit 14, a reference light generating unit 40, a balance detector 58, a K clock signal generating unit 82, a signal processing unit 60 (see FIG. 4), and a calculation unit 90 (see FIG. 3). The optical tomographic imaging apparatus 1 also includes an observation optical system 80 for observing the anterior segment of the subject's eye 100, and an alignment optical system (not shown) for aligning a measurement arm 26 (described below) and the observation optical system 80 to a predetermined positional relationship with respect to the subject's eye 100. Note that the alignment optical system can be one used in known optical tomographic imaging apparatuses, and therefore a detailed description thereof will be omitted.

[0022] The light source 11 is a wavelength sweep type light source, and the wavelength (wave number) of the emitted light changes at a predetermined cycle. Because the wavelength of the light irradiated onto the subject's eye 100 changes (sweeps), the intensity distribution of the light reflected from each part in the depth direction of the subject's eye 100 can be obtained by spectral analysis (for example, Fourier transform or discrete Fourier transform) of the signal obtained from the interference light between the reflected light from the subject's eye 100 and the reference light.

[0023] The SMFC 12 is connected to the light source 11 via an SMF (single mode fiber). The light output from the light source 11 passes through the SMF and is input to the SMFC 12. The light input to the SMFC 12 is demultiplexed by the SMFC 12, passes through the SMF, and is output to the SMFC 13 and the K clock signal generating unit 82, respectively.

[0024] The light input to SMFC 13 is demultiplexed by SMFC 13, passes through the SMF, and is output to measurement light generation unit 14 and reference light generation unit 40. Note that, hereinafter, the light output to measurement light generation unit 14 may be referred to as measurement light, and the light output to reference light generation unit 40 may be referred to as reference light.

[0025] The measurement light generation unit 14 will now be described. The measurement light generation unit 14 includes polarization control devices 15, 31, and 37, a first polarization-dependent delay line 16, SMFCs 24 and 25, a measurement arm 26, a calibration arm 32, an in-line polarizing beam splitter 38, and a first local oscillator 39.

[0026] The measurement light output from the SMFC 13 passes through the SMF and is input to the first polarization dependent delay line 16 via the polarization controller 15. The polarization controller 15 controls the polarization state of the measurement light.

[0027] The first polarization-dependent delay line 16 includes a collimator lens 17, a linear polarizer 18, a polarization beam spreader 19, mirrors 20 and 21, a mirror 22, and a lens 23. The measurement light output from the polarization controller 15 passes through the SMF and is output to the collimator lens 17. The measurement light output to the collimator lens 24 is output to the polarization beam spreader 19 via the linear polarizer 18. The linear polarizer 18 splits the measurement light into two beams of light having orthogonal polarization components (a horizontally polarized component and a horizontally polarized component). The polarization beam spreader 19 transmits the horizontally polarized component and reflects the vertically polarized component. The horizontally polarized component of the measurement light output from the linear polarizer 18 to the polarization beam spreader 19 passes through the polarization beam spreader 19 and is output to the mirror 20, reflected by the mirror 20, and output to the polarization beam spreader 19 again. The horizontally polarized component output to the polarized beam spreader 19 is transmitted through the polarized beam spreader 19 again and output to the mirror 22. The vertically polarized component of the measurement light output from the linear polarizer 18 to the polarized beam spreader 19 is reflected by the polarized beam spreader 19 and output to the mirror 21, and is reflected by the mirror 21 and output to the polarized beam spreader 19 again. The vertically polarized component output to the polarized beam spreader 19 is reflected by the polarized beam spreader 19 again and output to the mirror 22. The distance between the polarized beam spreader 19 and the mirror 20 is shorter than the distance between the polarized beam spreader 19 and the mirror 21. Therefore, the optical path length of the horizontally polarized component output to the mirror 22 is shorter than the optical path length of the vertically polarized component output to the mirror 22. The measurement light (hereinafter simply referred to as "measurement light") containing a horizontally polarized component and a vertically polarized component that is output to mirror 22 is input to SMF via lens 23, passes through the SMF, and is input to SMFC 24. The measurement light input to SMFC 24 is split by SMFC 24, passes through the SMF, and is output to SMFC 25 and polarization control device 37, respectively.

[0028] The measurement light input from SMFC 24 to SMFC 25 will now be described. The measurement light input to SMFC 25 is split by SMFC 25, passes through an SMF, and is output to measurement arm 26 and calibration arm 32 (more specifically, to calibration arm 32 via polarization control device 31). Hereinafter, the light output to measurement arm 26 will be referred to as measurement light, and the light output to calibration arm 32 will be referred to as calibration light. As described above, the measurement light input to SMFC 25 contains a horizontally polarized component and a vertically polarized component generated by first polarization-dependent delay line 16. Therefore, the measurement light output to measurement arm 26 contains a horizontally polarized component and a vertically polarized component, and the calibration light output to calibration arm 32 also contains a horizontally polarized component and a vertically polarized component.

[0029] The measurement arm 26 includes a collimator lens 27, a galvanometer scanner 28, a dichroic mirror 29, and an objective lens 30. The measurement light output from the SMFC 25 to the measurement arm 26 passes through the SMF and is emitted to the collimator lens 27. The measurement light emitted to the collimator lens 27 is emitted to the two-axis galvanometer scanner 28. The galvanometer scanner 28 is configured to be tilted by a second driver 85 (see FIG. 3 ). When the second driver 85 tilts the galvanometer scanner 28, the irradiation position of the measurement light on the subject's eye 100 is scanned laterally. The measurement light emitted from the galvanometer scanner 28 is reflected by the dichroic mirror 29. The dichroic mirror 29 transmits short-wavelength light including visible light, while reflecting near-infrared wavelength light including light from the light source 11. The measurement light reflected by the dichroic mirror 29 is irradiated onto the subject's eye 100 via the objective lens 30. The reflected light from the subject's eye 100 is emitted to the collimator lens 27 via the objective lens 30, the dichroic mirror 29, and the galvanometer scanner 28, in the reverse order to the above. The reflected light emitted to the collimator lens 27 is input to the SMF, passes through the SMF, and is input again to the SMFC 25. As described above, the measurement light input to the measurement arm 26 contains a horizontally polarized component and a vertically polarized component generated by the first polarization-dependent delay line 16. Hereinafter, the measurement light containing the horizontally polarized component will be referred to as horizontally polarized measurement light, and the measurement light containing the vertical component will be referred to as vertically polarized measurement light. The SMFC 25 receives the reflected light of the horizontally polarized measurement light reflected by the subject's eye 100 (hereinafter also referred to as horizontally polarized reflected light) and the reflected light of the vertically polarized measurement light reflected by the subject's eye 100 (hereinafter also referred to as vertically polarized reflected light).

[0030] Light (calibration light) is input to the calibration arm 32 from the SMFC 25 via the polarization control device 31. The calibration arm 32 includes a collimator lens 33, a glass block 34, a lens 35, and a mirror 36. The calibration light output from the polarization control device 31 passes through the SMF and is emitted to the collimator lens 33. The calibration light emitted to the collimator lens 33 is then emitted toward the lens 35. The glass block 34 is disposed between the collimator lens 33 and the lens 35. The glass block 34 is disposed so that a portion of the calibration light emitted from the collimator lens 33 (approximately the lower half of the light in FIG. 1) passes through the glass block 34. As a result, a portion of the calibration light emitted from the collimator lens 33 (light passing downward in FIG. 1) passes through the glass block 34 and is irradiated onto the mirror 36 via the lens 35. Meanwhile, the other portion of the calibration light emitted from collimator lens 33 (light passing upward in FIG. 1 ) is irradiated onto mirror 36 via lens 35 without passing through glass block 34. The light reflected from mirror 36 passes through lens 35, with a portion of it passing through glass block 34 and being emitted to collimator lens 33, and the other portion being emitted to collimator lens 33 without passing through glass block 34. The reflected light emitted to collimator lens 33 is then input to the SMF, passes through the SMF, and is then input again to SMFC 25 via polarization controller 31. The SMFC 25 receives the calibration light that has passed through glass block 34 and the calibration light that has not passed through glass block 34. As described above, the calibration light input to calibration arm 32 contains the horizontally polarized component and the vertically polarized component generated in first polarization-dependent delay line 16. Therefore, the calibration light input to calibration arm 32 and then input again to SMFC 25 also contains the horizontally polarized component and the vertically polarized component.

[0031] The reflected light from the eye 100 and the calibration light input to the SMFC 25 pass through the SMF and are input again to the SMFC 24. The reflected light from the eye 100 and the calibration light input to the SMFC 24 pass through the SMF and are input to the SMFC 57.

[0032] Next, the light input from the SMFC 24 to the polarization control device 37 will be described. The light output from the SMFC 24 to the polarization control device 37 passes through the SMF and is output to the in-line polarization beam splitter 38 via the polarization control device 37. A first local oscillator 39 is connected to the in-line polarization beam splitter 38, which splits the light into two lights with a phase difference of 180 degrees and outputs them to the first local oscillator 39. The first local oscillator 39 optically generates a signal for frequency conversion and outputs the generated signal (hereinafter also referred to as a first local oscillator signal) to the signal processing unit 60 (see FIG. 4).

[0033] Next, we will explain the reference light generation unit 40. The reference light generation unit 40 includes a polarization control device 41, a second polarization dependent delay line 42, an SMFC 50, a reference variable delay line 51, an in-line polarizing beam splitter 55, and a second local oscillator 56.

[0034] The reference light output from the SMFC 13 passes through the SMF, and is input to the second polarization dependent delay line 42 via the polarization controller 41 .

[0035] The second polarization dependent delay line 42 includes a collimator lens 43, a linear polarizer 44, a polarization beam spreader 45, mirrors 46 and 47, a mirror 48, and a lens 49. The reference light output from the polarization controller 41 passes through the SMF and is output to the collimator lens 43. The reference light output to the collimator lens 43 is split by the linear polarizer 44 into two light beams having orthogonal polarization components (a horizontally polarized component and a horizontally polarized component), which are output to the polarization beam spreader 45. The horizontally polarized component of the reference light output to the polarization beam spreader 45 passes through the polarization beam spreader 45 and is output to the mirror 46, reflected by the mirror 46, and output to the polarization beam spreader 45 again. The horizontally polarized component output to the polarization beam spreader 45 passes through the polarization beam spreader 45 again and is output to the mirror 48. Furthermore, the vertically polarized component of the reference light emitted to polarizing beam spreader 45 is reflected by polarizing beam spreader 45 and emitted to mirror 47, and is reflected by mirror 47 and emitted to polarizing beam spreader 45 again. The vertically polarized component emitted to polarizing beam spreader 45 is reflected again by polarizing beam spreader 45 and emitted to mirror 48. The distance between polarizing beam spreader 45 and mirror 46 is longer than the distance between polarizing beam spreader 45 and mirror 47. Therefore, the optical path length of the horizontally polarized component of the reference light is longer than the optical path length of the vertically polarized component of the reference light. The reference light (hereinafter simply referred to as "reference light") emitted to mirror 48 and including the horizontally polarized component and the vertically polarized component is input to SMF via lens 49, passes through the SMF, and is input to SMFC 50. The reference light input to SMFC 50 is split by SMFC 50 and output to reference variable delay line 51 and in-line polarizing beam splitter 55, respectively.

[0036] The reference variable delay line 51 includes collimator lenses 52 and 54 and a reference mirror 53. The reference light output from the SMFC 50 to the reference variable delay line 51 passes through the SMF and is emitted to the collimator lens 52. The reference light emitted to the collimator lens 52 is reflected by the reference mirror 53 and is emitted to the collimator lens 54. The reference mirror 53 is configured to move forward and backward relative to the collimator lenses 52 and 54 by a third driving device 86 (see FIG. 3). The third driving device 86 moves the reference mirror 53, thereby changing the optical path length of the reference light. In this embodiment, before measurement is started, the position of the reference mirror 53 is adjusted so that the signal from the subject's eye 100 falls within the measurement range of the OCT in the depth direction. Furthermore, the position of the reference mirror 53 is adjusted so that, of the horizontally polarized component and the vertically polarized component generated by the second polarization-dependent delay line 42, the difference between the optical path length of the horizontally polarized component and the optical path length of the light reflected from the subject's eye 100 is shorter than the difference between the optical path length of the vertically polarized component and the optical path length of the light reflected from the subject's eye 100. The reflected light output to the collimator lens 54 is input to the SMF, passes through the SMF, and is input to the SMFC 57. As described above, the reference light input to the reference variable delay line 51 includes the horizontally polarized component and the vertically polarized component generated by the second polarization-dependent delay line 42. Therefore, the reference light input to the SMFC 57 includes a horizontally polarized component (hereinafter also referred to as horizontally polarized reference light) and a vertically polarized component (hereinafter also referred to as vertically polarized reference light).

[0037] Next, a description will be given of the light output from the SMFC 50 to the in-line polarizing beam splitter 55. The light output from the SMFC 50 to the in-line polarizing beam splitter 55 is split by the in-line polarizing beam splitter 55 into two lights with a phase difference of 180 degrees, which are output to the second local oscillator 56. The second local oscillator 56 optically generates a signal for frequency conversion, and outputs the generated signal (hereinafter also referred to as a second local oscillator signal) to the signal processing unit 60 (see FIG. 4).

[0038] The SMFC 57 receives the reflected light from the eye 100 and the calibration light generated by the measurement light generation unit 14, as well as the reference light generated by the reference light generation unit 40. The SMFC 57 combines the reflected light from the eye 100, the calibration light, and the reference light to generate interference light. The SMFC 57 splits the interference light into two interference lights with a phase difference of 180 degrees, and outputs them to a balance detector 58. The balance detector 58 performs differential amplification and noise reduction processing on the two input interference lights, converts them into electrical signals (interference signals), and outputs the interference signals to a signal processing unit 60 (see FIG. 4). The processing of the interference signals by the signal processing unit 60 will be described in detail later.

[0039] Here, the interference signal generated in this embodiment will be described. As described above, in this embodiment, the measurement light generating unit 14 separates the measurement light into a horizontally polarized component and a vertically polarized component, and the reference light generating unit 40 separates the reference light into a horizontally polarized component and a vertically polarized component. Since multiple types of light with different vibration directions are input to the SMFC 57, the SMFC 57 generates multiple types of interference light with different vibration directions, converts the generated interference light into an interference signal, and outputs it to the signal processing unit 60 (see FIG. 4).

[0040] Specifically, in the measurement light generating unit 14, the horizontally polarized measurement light and the vertically polarized measurement light generated by the first polarization-dependent delay line 16 are irradiated onto the test eye 100. When the horizontally polarized measurement light is irradiated onto the test eye 100, it is scattered by the test eye 100. Not only the test eye 100 but also living organisms contain birefringent media such as fibrous tissue and depolarized media such as melanosomes. For this reason, the horizontally polarized reflected light (the horizontally polarized measurement light reflected by the test eye 100) is generally light vibrating in various directions. Similarly, the vertically polarized reflected light (the vertically polarized measurement light reflected by the test eye 100) is also generally light vibrating in various directions. The horizontally polarized reflected light and the vertically polarized reflected light are input to the SMFC 57 as return light from the test eye 100. SMFC 57 also receives as input the horizontally polarized reference light and the vertically polarized reference light generated by second polarization-dependent delay line 42 of reference light generation unit 40. SMFC 57 generates interference light resulting from interference between the horizontally polarized component of the horizontally polarized reflected light and the horizontally polarized reference light (hereinafter, the interference signal converted from this interference light will be referred to as interference signal HH), interference light resulting from interference between the vertically polarized component of the horizontally polarized reflected light and the vertically polarized reference light (hereinafter, the interference signal converted from this interference light will be referred to as interference signal HV), interference light resulting from interference between the horizontally polarized component of the vertically polarized reflected light and the horizontally polarized reference light (hereinafter, the interference signal converted from this interference light will be referred to as interference signal VH), and interference light resulting from interference between the vertically polarized component of the vertically polarized reflected light and the vertically polarized reference light (hereinafter, the interference signal converted from this interference light will be referred to as interference signal VV).

[0041] In this embodiment, the first polarization-dependent delay line 16 of the measurement light generation unit 14 is adjusted so that the horizontally polarized measurement light and the vertically polarized measurement light have different optical path lengths. The second polarization-dependent delay line 42 of the reference light generation unit 40 is also adjusted so that the horizontally polarized reference light and the vertically polarized reference light have different optical path lengths. This adjustment allows four interference signals HH, VH, HV, and VV to be detected at different depth positions in the axial direction, as shown in FIG. 2. In FIG. 2, the origin position "0" indicates direct current (DC), and the zero point, which serves as the reference for the depth position, coincides with "0."

[0042] Specifically, in the first polarization-dependent delay line 16, the optical path length of the horizontally polarized measurement light is made shorter than the optical path length of the vertically polarized measurement light. Therefore, for the two interference signals HH and VH obtained by converting the interference light generated by interference with the horizontally polarized reference light, the interference signal HH is detected at a position shallower than the interference signal VH. Similarly, for the two interference signals HV and VV obtained by converting the interference light generated by interference with the vertically polarized reference light, the interference signal HV is detected at a position shallower than the interference signal VV. Furthermore, in the second polarization-dependent delay line 42, the optical path length of the horizontally polarized reference light is made longer than the optical path length of the vertically polarized reference light. Furthermore, as described above, the difference between the optical path length of the horizontally polarized reference light and the optical path length of the light reflected from the test eye 100 is made shorter than the difference between the optical path length of the vertically polarized reference light and the optical path length of the light reflected from the test eye 100. Therefore, the interference signals HH and VH obtained by converting the interference light generated by interference with the horizontally polarized reference light are detected closer to the zero point than the interference signals HV and VV obtained by converting the interference light generated by interference with the vertically polarized reference light. Therefore, as shown in Figure 2, the four interference signals HH, VH, HV, and VV are detected separately so that the interference signals HH, VH, HV, and VV are located deeper from the zero point in this order.

[0043] As shown in FIG. 2, in this embodiment, the interference signal HH is generated from the zero point to the frequency f of the K clock signal (described later). k Half of (frequency f k / 2) at frequency f k / 2 is called the Nyquist frequency. In this embodiment, the frequency corresponding to the optical path length difference between the horizontally polarized measurement light and the vertically polarized measurement light is called frequency f1, and the frequency corresponding to the optical path length difference between the horizontally polarized reference light and the vertically polarized reference light is called frequency f2. In this embodiment, frequency f2 is approximately twice frequency f1, but is not limited to this configuration. For example, frequency f1+f k The frequency f1+f k In this embodiment, the interval between frequency f2 and frequency f2+f k / 2.

[0044] As shown in FIG. 1 , the observation optical system 80 irradiates the subject's eye 100 with observation light via the dichroic mirror 29 and captures the reflected light reflected from the anterior segment of the subject's eye 100 (i.e., the reflected light of the irradiated observation light). The light source of the observation optical system 80 outputs short-wavelength light including visible light. As described above, the dichroic mirror 29 reflects near-infrared wavelength light including light from the light source 11, while transmitting short-wavelength light including visible light (i.e., the observation light). Therefore, the optical tomographic imaging apparatus 1 of this embodiment can simultaneously measure the polarization characteristics of the subject's eye 100 and observe the subject's eye 100 using the observation optical system 80. Note that the observation optical system 80 can be one used in known optical tomographic imaging apparatuses, and therefore a detailed description of its configuration will be omitted.

[0045] The K clock signal generating unit 82 optically generates a sample clock (K clock) signal from the light branched from the SMFC 12 in order to sample the interference signal at equal frequency intervals (equal intervals relative to changes in the frequency of the light). In this embodiment, the K clock signal generating unit 82 is a Mach-Zehnder interferometer. Note that the K clock signal generating unit 82 can be a unit used in known optical tomographic imaging devices, and therefore a detailed description of its configuration will be omitted. The K clock signal generated by the K clock signal generating unit 82 is output to the calculation unit 90. Sampling the interference signal using the K clock signal suppresses distortion of the interference signal and prevents deterioration of resolution.

[0046] The optical tomographic imaging apparatus 1 of this embodiment also includes a position adjustment mechanism 87 (see FIG. 3) for adjusting the position of the optical tomographic imaging apparatus 1 with respect to the subject's eye 100, and a first driving device 84 (see FIG. 3) for driving the position adjustment mechanism 87. The first driving device 84 drives the position adjustment mechanism 87 in response to the examiner's operation of an operating member, thereby adjusting the position of the optical tomographic imaging apparatus 1 in the xy directions (vertical and horizontal directions) and the z direction (direction of forward and backward movement) with respect to the subject's eye 100.

[0047] Next, the configuration of the control system of the optical tomographic imaging apparatus 1 of this embodiment will be described. As shown in FIG. 3, the optical tomographic imaging apparatus 1 is controlled by a calculation unit 90. The calculation unit 90 is configured by a microcomputer (microprocessor) including a CPU, ROM, RAM, etc. The calculation unit 90 is connected to the light source 11, a first driver 84, a second driver 85, a third driver 86, a first data acquisition unit 64 (see FIG. 4), and a second data acquisition unit 75 (see FIG. 4). The calculation unit 90 controls the on / off of the light source 11, controls the first driver 84 to drive the position adjustment mechanism 87, controls the second driver 85 to drive the galvanometer scanner 28, and controls the third driver 86 to drive the reference mirror 53. The calculation unit 90 also acquires interference signals from the first data acquisition unit 64 and the second data acquisition unit 75.

[0048] Next, we will explain the processing of interference signals HH, VH, HV, and VV in signal processing unit 60. As shown in Fig. 4, interference signals HH, VH, HV, and VV output from balance detector 58 to signal processing unit 60 are input to power splitter 61 and electrically split by power splitter 61. The interference signals HH, VH, HV, and VV split by power splitter 61 are output to power splitter 62 and high-pass filter 70, respectively.

[0049] The interference signals HH, VH, HV, and VV output to the power splitter 62 are split by the power splitter 62 and output to a low-pass filter 63 and a high-pass filter 65, respectively.

[0050] The interference signals HH, VH, HV, and VV output from the power splitter 62 to the low-pass filter 63 will be described. The low-pass filter 63 receives the interference signals HH, VH, HV, and VV at a frequency f k The low-pass filter 63 attenuates signals with frequencies higher than f / 2 among the four interference signals HH, VH, HV, and VV. kThe low-pass filter 63 passes only the interference signal HH (see FIG. 2) having a frequency equal to or lower than 1 / 2 and outputs it to the first data acquisition unit 64. The first data acquisition unit 64 has two channels (hereinafter also referred to as channels A and B). The low-pass filter 63 outputs the interference signal HH to channel A of the first data acquisition unit 64.

[0051] Next, the interference signals HH, VH, HV, and VV output from the power splitter 62 to the high-pass filter 65 will be described. The high-pass filter 65 attenuates signals with frequencies lower than frequency f1. Of the four interference signals HH, VH, HV, and VV, the high-pass filter 65 passes three interference signals VH, HV, and VV (see FIG. 2) that have frequencies equal to or higher than frequency f1, and outputs them to the first frequency converter 66.

[0052] The first frequency converter 66 receives as input the interference signals (more specifically, the three interference signals VH, HV, and VV) output from the balance detector 58 to the signal processing unit 60 and the first local oscillator signal output from the first local oscillator 39 to the signal processing unit 60. The first local oscillator signal output from the first local oscillator 39 to the signal processing unit 60 is input to a bandpass filter 67. The bandpass filter 67 filters the first local oscillator signal so that frequency f1 becomes the center of its transmission frequency. The bandpass filter 67 outputs the filtered first local oscillator signal to a power splitter 68. The first local oscillator signal output to the power splitter 68 is split by the power splitter 68 and output to the first frequency converter 66 and the third frequency converter 77, respectively.

[0053] The first frequency converter 66 generates signals at the sum frequency and the difference frequency between the three input interference signals VH, HV, and VV and the first local oscillator signal. The frequency of the first local oscillator signal is frequency f1. Therefore, the three interference signals VH, HV, and VV are converted into signals having frequencies higher by frequency f1 (i.e., signals upconverted by frequency f1) and signals having frequencies lower by frequency f1 (i.e., signals downconverted by frequency f1).

[0054] The first frequency converter 66 outputs the generated signal to the low-pass filter 69. The low-pass filter 69 converts the frequency f k The signals with frequencies higher than f / 2 are attenuated. The signals obtained by up-converting the interference signals VH, HV, and VV by the frequency f1 are attenuated at the frequency f k 2. Therefore, the signals obtained by up-converting the interference signals VH, HV, and VV by the frequency f1 are all attenuated. On the other hand, the signals obtained by down-converting the interference signals VH, HV, and VV by the frequency f1 are converted so that the frequency f1 in FIG. 2 becomes DC (i.e., 0). Therefore, the low-pass filter 69 attenuates the signals obtained by down-converting the interference signals VH, HV, and VV by the frequency f1. k Only the signal obtained by down-converting the interference signal VH, which has a frequency of 1 / 2 or less, by the frequency f1 passes through.

[0055] The interference signal VH that has passed through the low-pass filter 69 is down-converted by the frequency f1 and output to the first data acquisition unit 64 (hereinafter simply referred to as the interference signal VH). As described above, the first data acquisition unit 64 has two channels A and B. The low-pass filter 69 outputs to channel B of the first data acquisition unit 64 the signal that has been down-converted by the frequency f1 from the interference signal VH.

[0056] In this embodiment, the interference signal VH is down-converted by frequency f1 so that the interference signal VH is in the same frequency band as the interference signal HH, and the two interference signals HH and VH are acquired by two different channels A and B of the first data acquisition unit 64. By down-converting the interference signal VH, the first data acquisition unit 64 can acquire the two interference signals HH and VH in the same frequency band.

[0057] Next, the interference signals HH, VH, HV, and VV output from the power splitter 61 to the high-pass filter 70 will be described. The high-pass filter 70 attenuates signals with frequencies lower than frequency f2. Of the four interference signals HH, VH, HV, and VV, the high-pass filter 70 passes two interference signals HV and VV (see FIG. 2) that have frequencies equal to or higher than frequency f2, and outputs them to the second frequency converter 71.

[0058] The second frequency converter 71 receives as input the interference signal (more specifically, the two interference signals HV and VV) output from the balance detector 58 to the signal processing unit 60 and the second local oscillator signal output from the second local oscillator 56 to the signal processing unit 60. The second local oscillator signal output from the second local oscillator 56 to the signal processing unit 60 is input to a bandpass filter 72. The bandpass filter 72 filters the second local oscillator signal so that frequency f2 becomes the center of its transmission frequencies. The bandpass filter 72 outputs the filtered second local oscillator signal to the second frequency converter 71.

[0059] The second frequency converter 71 generates signals of the sum frequency and the difference frequency between the two input interference signals HV, VV and the second local oscillator signal. The frequency of the second local oscillator signal is frequency f2. Therefore, the two interference signals HV, VV are converted into a signal having a frequency higher by frequency f2 (i.e., a signal up-converted by frequency f2) and a signal having a frequency lower by frequency f2 (i.e., a signal down-converted by frequency f2).

[0060] The second frequency converter 71 outputs the generated signal to the power splitter 73. The signal output to the power splitter 73 is split by the power splitter 73 and output to a low-pass filter 74 and a high-pass filter 76, respectively.

[0061] The low-pass filter 74 is k The interference signals HV and VV are up-converted by frequency f2 and attenuate signals with frequencies higher than f k2. Therefore, the signals obtained by up-converting the interference signals HV and VV by the frequency f2 are all attenuated. On the other hand, the signals obtained by down-converting the interference signals HV and VV by the frequency f2 are converted so that the frequency f2 in FIG. 2 becomes DC (i.e., 0). Therefore, the low-pass filter 74 attenuates the signals obtained by down-converting the interference signals HV and VV by the frequency f2. k Only the signal obtained by down-converting the interference signal HV, which has a frequency of 1 / 2 or less, by the frequency f2 passes through.

[0062] The interference signal HV that has passed through the low-pass filter 74 is down-converted by frequency f2 to produce a signal (hereinafter simply referred to as the interference signal HV) that is output to the second data acquisition unit 75. The second data acquisition unit 75 has two channels (hereinafter also referred to as channels C and D). The low-pass filter 74 outputs the interference signal HV to channel C of the second data acquisition unit 75.

[0063] Next, the signal output from the power splitter 73 to the high-pass filter 76 will be described. The high-pass filter 76 receives the signals obtained by up-converting the interference signals HV and VV by frequency f2 in the second frequency converter 71, and the signals obtained by down-converting the interference signals HV and VV by frequency f2. The high-pass filter 76 attenuates signals with frequencies lower than frequency f1. The signals obtained by up-converting the interference signals HV and VV by frequency f2 have frequencies higher than frequency f1 before being up-converted (see FIG. 2). For this reason, the high-pass filter 76 passes the signals obtained by up-converting the interference signals HV and VV by frequency f2. On the other hand, the signals obtained by down-converting the interference signals HV and VV by frequency f2 are converted so that frequency f2 in FIG. 2 becomes DC (i.e., 0). For this reason, the high-pass filter 76 attenuates the signal obtained by down-converting the interference signals HV and VV by frequency f2, that is, the interference signal HV having a frequency lower than frequency f1, by frequency f2, and passes the signal obtained by down-converting the interference signal VV having a frequency equal to or higher than frequency f1 by frequency f2 (see FIG. 2). Therefore, the high-pass filter 76 passes the signal obtained by up-converting the interference signals HV and VV by frequency f2 and the signal obtained by down-converting the interference signal VV by frequency f2, and outputs them to the third frequency converter 77.

[0064] The third frequency converter 77 receives as input the interference signal output from the balance detector 58 to the signal processing unit 60 (more specifically, the signal obtained by upconverting the interference signals HV and VV by frequency f2, and the signal obtained by downconverting the interference signal VV by frequency f2), and the first local oscillator signal output from the first local oscillator 39 to the signal processing unit 60 (more specifically, the first local oscillator signal output from the power splitter 68 to the third frequency converter 77).

[0065] The third frequency converter 77 generates signals at the sum frequency and difference frequency between the first local oscillator signal and the signals obtained by up-converting the input interference signals HV and VV by frequency f2 and the signals obtained by down-converting the interference signal VV by frequency f2. The frequency of the first local oscillator signal is frequency f1. Therefore, the signals obtained by up-converting the interference signals HV and VV by frequency f2 and the signals obtained by down-converting the interference signal VV by frequency f2 are converted into signals having a frequency higher by frequency f1 and signals having a frequency lower by frequency f1. In detail, the third frequency converter 77 generates a signal obtained by upconverting the interference signals HV and VV by frequency f2 and then further upconverting it by frequency f1 (a signal obtained by upconverting the interference signals HV and VV by frequency f1+f2), a signal obtained by upconverting the interference signals HV and VV by frequency f2 and then further downconverting it by frequency f1 (a signal obtained by converting the interference signals HV and VV by frequency f2-f1, i.e., a signal obtained by upconverting the interference signals HV and VV by frequency f1), a signal obtained by downconverting the interference signal VV by frequency f2 and then further upconverting it by frequency f1 (a signal obtained by converting the interference signal VV by frequency f1-f2, i.e., a signal obtained by downconverting the interference signal VV by frequency f1), and a signal obtained by downconverting the interference signal VV by frequency f2 and then further downconverting it by frequency f1 (a signal obtained by downconverting the interference signal VV by frequency f1+f2).

[0066] The third frequency converter 77 outputs the generated signal to the low-pass filter 78. The low-pass filter 78 converts the frequency f k The signals obtained by up-converting the interference signals HV and VV by the frequency f1+f2, the signals obtained by up-converting the interference signals HV and VV by the frequency f1, and the signals obtained by down-converting the interference signal VV by the frequency f1 are attenuated at the frequency f k / 2 (see FIG. 2). Therefore, the signals obtained by up-converting the interference signals HV and VV by the frequency f1+f2 and the signals obtained by up-converting the interference signals HV and VV by the frequency f1 are all attenuated. On the other hand, the signal obtained by down-converting the interference signal VV by the frequency f1+f2 is converted so that the frequency f1+f2 in FIG. 2 becomes DC (i.e., 0). Therefore, the low-pass filter 78 passes only the signal obtained by down-converting the interference signal VV by the frequency f1+f2.

[0067] The interference signal VV that has passed through the low-pass filter 78 is down-converted by frequency f1+f2 to produce a signal (hereinafter simply referred to as interference signal VV) that is output to the second data acquisition unit 75. As described above, the second data acquisition unit 75 has two channels C and D. The low-pass filter 78 outputs the interference signal VV to channel D of the second data acquisition unit 75.

[0068] In this embodiment, the interference signals HV and VV are each down-converted to have the same frequency band as the interference signal HH, and the two interference signals HV and VV are respectively acquired on two different channels C and D of the second data acquisition unit 75. By down-converting the interference signals HV and VV, the second data acquisition unit 75 can acquire the interference signals HV and VV in the same frequency band as the two interference signals HH and VH. Furthermore, since the four interference signals HH, VH, HV, and VV can be detected in the same frequency band (i.e., a frequency band smaller than the Nyquist frequency), the detection sensitivity of the four interference signals HH, VH, HV, and VV can be improved. Furthermore, by down-converting the four interference signals HH, VH, HV, and VV to have the same frequency band, the first data acquisition unit 64 and the second data acquisition unit 75 can be configured using the same type of data acquisition unit.

[0069] Next, a process for correcting the detection position using an interference signal generated from the calibration light will be described. The calibration light is used to correct deviations in sampling timing that occur between the four channels A to D of the first data acquisition unit 64 and the second data acquisition unit 75. A trigger signal is input to the first data acquisition unit 64 and the second data acquisition unit 75 so that the four channels A to D start sampling in synchronization. However, due to an error in the K clock signal generation unit 82, the timing at which the trigger signal arrives at each of the four channels A to D may differ. This results in deviations in the sampling timing of the four channels A to D. The calculation unit 90 executes a process for correcting such deviations in sampling timing using the calibration light. Note that the process for correcting deviations in sampling timing that occur between the four channels A to D using the calibration light can be performed using a known method, such as that disclosed in Japanese Patent Application Laid-Open No. 2019-113398, and therefore a detailed description thereof will be omitted.

[0070] In this embodiment, the interference signals HH, VH, HV, and VV are processed using the signal processing unit 60 shown in Fig. 4, but the present invention is not limited to such a configuration. It is sufficient that the four interference signals HH, VH, HV, and VV can be down-converted so that they are in the same frequency band, and for example, the interference signals HH, VH, HV, and VV may be processed using the signal processing unit 160 shown in Fig. 5 or the signal processing unit 260 shown in Fig. 6.

[0071] First, we will explain the processing of interference signals HH, VH, HV, and VV by signal processing unit 160 shown in Fig. 5. As shown in Fig. 5, interference signals HH, VH, HV, and VV output from balance detector 58 to signal processing unit 160 are split by power splitter 161 and output to power splitter 162 and power splitter 170, respectively. Interference signals HH, VH, HV, and VV output to power splitter 162 are split by power splitter 162 and output to low-pass filter 163 and high-pass filter 165, respectively.

[0072] The interference signals HH, VH, HV, and VV whose frequencies have not been converted are input to the low-pass filter 163. The low-pass filter 163 filters out the interference signals HH, VH, HV, and VV whose frequencies have not been converted. k Only the interference signal HH (see FIG. 2) having a frequency equal to or lower than 1 / 2 is passed through and output to channel A of the first data acquisition unit 64.

[0073] Next, the interference signals HH, VH, HV, and VV output from the power splitter 162 to the high-pass filter 165 will be described. The high-pass filter 165 passes three interference signals VH, HV, and VV (see FIG. 2) of the interference signals HH, VH, HV, and VV that have frequencies equal to or higher than frequency f1, and outputs them to the first frequency converter 166. A first local oscillator signal is also output to the first frequency converter 166, as will be described later. The first frequency converter 166 up-converts and down-converts the three interference signals VH, HV, and VV by frequency f1, which is the frequency of the first local oscillator signal, and outputs them to the low-pass filter 169. The low-pass filter 169 ... filters out the interference signals VH, HV, and VV up-converted by frequency f1 and the interference signals VH, HV, and VV down-converted by frequency f1, and outputs the interference signals VH, HV, and VV down-converted by frequency f1. k The first data acquisition unit 64 passes only the signal obtained by down-converting the interference signal VH, which has a frequency equal to or lower than / 2, by the frequency f1 (see FIG. 2).

[0074] Here, the path of the first local oscillator signal input to the first frequency converter 166 will be described. The first local oscillator signal output from the first local oscillator 39 to the signal processing unit 60 is input to the bandpass filter 167, where it is filtered so that frequency f1 becomes the center of its transmission frequency. The filtered first local oscillator signal is split by the power splitter 168 and output to the first frequency converter 166 and the fourth frequency converter 179, respectively. The first local oscillator signal output to the first frequency converter 166 is used for frequency conversion of the three interference signals VH, HV, and VV in the first frequency converter 166, as described above.

[0075] Next, a description will be given of the interference signals HH, VH, HV, and VV output from power splitter 161 to power splitter 170. The interference signals HH, VH, HV, and VV output to power splitter 170 are split by power splitter 170 and output to high-pass filter 171 and high-pass filter 177, respectively.

[0076] The high-pass filter 171 passes two interference signals HV and VV (see FIG. 2) of the interference signals HH, VH, HV, and VV, which have frequencies equal to or higher than frequency f2, and outputs them to the second frequency converter 172. A second local oscillator signal is also output to the second frequency converter 172, as will be described later. The second frequency converter 172 up-converts and down-converts the two interference signals HV and VV by frequency f2, which is the frequency of the second local oscillator signal, and outputs them to the low-pass filter 176. The low-pass filter 176 passes the interference signals HV and VV up-converted by frequency f2 and the down-converted interference signals HV and VV, which have frequencies equal to or higher than frequency f2. k The second data acquisition unit 75 passes only the signal obtained by down-converting the interference signal HV, which has a frequency equal to or lower than f2, by the frequency f2 (see FIG. 2).

[0077] Here, the path of the second local oscillator signal input to the second frequency converter 172 will be described. The second local oscillator signal output from the second local oscillator 56 to the signal processing unit 60 is input to the bandpass filter 173, where it is filtered so that frequency f2 becomes the center of its transmission frequency. The filtered second local oscillator signal is split by the power splitter 174 and output to the second frequency converter 172 and the fourth frequency converter 179, respectively. The second local oscillator signal output to the second frequency converter 172 is used for frequency conversion of the two interference signals HV and VV in the second frequency converter 172, as described above.

[0078] Next, the interference signals HH, VH, HV, and VV output from power splitter 170 to high-pass filter 177 will be described. High-pass filter 177 attenuates signals with frequencies lower than frequency f1+f2. Of the four interference signals HH, VH, HV, and VV, high-pass filter 177 passes only interference signal VV (see FIG. 2), which has a frequency equal to or higher than frequency f1+f2, and outputs this to third frequency converter 178.

[0079] The third frequency converter 178 also outputs a signal generated by a fourth frequency converter 179. The signal generated by the fourth frequency converter 179 will now be described. The fourth frequency converter 179 receives the filtered first local oscillator signal split by the power splitter 168 and the filtered second local oscillator signal split by the power splitter 174. The fourth frequency converter 179 generates signals at the sum frequency and difference frequency between the input first and second local oscillator signals. The frequency of the first local oscillator signal is frequency f1, and the frequency of the second local oscillator signal is frequency f2. Therefore, the fourth frequency converter 179 generates a local oscillator signal having a frequency f1+f2 and a local oscillator signal having a frequency f1 (frequency f2-f1). The fourth frequency converter 179 outputs the generated local oscillator signal having frequency f1+f2 and the local oscillator signal having frequency f1 to the band-pass filter 180. The bandpass filter 180 filters the signal so that the center of its transmission frequency is the frequency f1+f2. Therefore, the bandpass filter 180 filters only the local oscillator signal having the frequency f1+f2 (hereinafter also referred to as the third local oscillator signal) and outputs it to the third frequency converter 178.

[0080] The third frequency converter 178 generates signals at the sum frequency and difference frequency between the input interference signal VV and the third local oscillator signal. The frequency of the third local oscillator signal is frequency f1+f2. Therefore, the interference signal VV is converted into a signal that is up-converted by frequency f1+f2 and a signal that is down-converted by frequency f1+f2.

[0081] The third frequency converter 178 outputs the generated signal to the low-pass filter 181. The low-pass filter 181 converts the frequency f k The low-pass filter 181 attenuates signals with frequencies higher than f / 2 out of the interference signal VV up-converted by the frequency f1+f2 and the signal down-converted by the frequency f1+f2. k The second data acquisition unit 75 passes only the interference signal VV (see FIG. 2) that has been down-converted by frequency f1+f2, which is a frequency equal to or lower than f1 / 2, and outputs the signal to channel D of the second data acquisition unit 75.

[0082] From the above, even if the interference signals HH, VH, HV, and VV are processed using the signal processing unit 160 shown in Figure 5, the four interference signals HH, VH, HV, and VV can each be downconverted to the same frequency, and the first data acquisition unit 64 and the second data acquisition unit 75 can acquire the four interference signals HH, VH, HV, and VV in the same frequency band.

[0083] Next, we will explain the processing of interference signals HH, VH, HV, and VV by signal processing unit 260 shown in Fig. 6. As shown in Fig. 6, interference signals HH, VH, HV, and VV output from balance detector 58 to signal processing unit 260 are split by power splitter 261 and output to power splitter 262 and power splitter 270, respectively. Interference signals HH, VH, HV, and VV output to power splitter 262 are split by power splitter 262 and output to low-pass filter 263 and high-pass filter 265, respectively.

[0084] The interference signals HH, VH, HV, and VV whose frequencies have not been converted are input to the low-pass filter 263. The low-pass filter 263 filters out the interference signals HH, VH, HV, and VV whose frequencies have not been converted. k Only the interference signal HH (see FIG. 2) having a frequency equal to or lower than 1 / 2 is passed through and output to channel A of the first data acquisition unit 64.

[0085] Next, the interference signals HH, VH, HV, and VV output from the power splitter 262 to the high-pass filter 265 will be described. The high-pass filter 265 passes three interference signals VH, HV, and VV (see FIG. 2) of the interference signals HH, VH, HV, and VV that have frequencies equal to or higher than frequency f1, and outputs them to the first frequency converter 266. A first local oscillator signal is also output to the first frequency converter 266, as will be described later. The first frequency converter 266 up-converts and down-converts the three interference signals VH, HV, and VV by frequency f1, which is the frequency of the first local oscillator signal, and outputs them to the low-pass filter 269. The low-pass filter 269 passes only the interference signals VH, HV, and VV that have been up-converted by frequency f1 and the interference signals VH, HV, and VV that have been down-converted by frequency f1. k The first data acquisition unit 64 passes only the interference signal VH (see FIG. 2) that has been down-converted by frequency f1, which is a frequency equal to or lower than / 2, and outputs the signal to channel B of the first data acquisition unit 64.

[0086] Here, the path of the first local oscillator signal input to the first frequency converter 266 will be described. The first local oscillator signal output from the first local oscillator 39 to the signal processing unit 60 is input to the bandpass filter 267 and filtered by the bandpass filter 267 so that frequency f1 becomes the center of the transmission frequency. The filtered first local oscillator signal is split by the power splitter 268 and output to the first frequency converter 266 and the third frequency converter 278, respectively. The first local oscillator signal output to the first frequency converter 266 is used for frequency conversion of the three interference signals VH, HV, and VV in the first frequency converter 266, as described above.

[0087] Next, a description will be given of interference signals HH, VH, HV, and VV output from power splitter 261 to power splitter 270. Interference signals HH, VH, HV, and VV output to power splitter 270 are split by power splitter 270 and output to high-pass filter 271 and high-pass filter 277, respectively.

[0088] The high-pass filter 271 passes two interference signals HV and VV (see FIG. 2) of the interference signals HH, VH, HV, and VV, which have frequencies equal to or higher than frequency f2, and outputs them to the second frequency converter 272. A second local oscillator signal is also output to the second frequency converter 272, as will be described later. The second frequency converter 272 up-converts and down-converts the two interference signals HV and VV by frequency f2, which is the frequency of the second local oscillator signal, and outputs them to the low-pass filter 276. The low-pass filter 276 passes only the interference signals HV and VV up-converted by frequency f2 and the interference signals HV and VV down-converted by frequency f2. k The second data acquisition unit 75 passes only the interference signal HV (see FIG. 2) that has been down-converted by frequency f2, which is a frequency equal to or lower than f / 2, and outputs the signal to channel C of the second data acquisition unit 75.

[0089] Here, the path of the second local oscillator signal input to the second frequency converter 272 will be described. The second local oscillator signal output from the second local oscillator 56 to the signal processing unit 60 is input to the bandpass filter 273, where it is filtered so that frequency f2 becomes the center of its transmission frequency. The filtered second local oscillator signal is split by the power splitter 274 and output to the second frequency converter 272 and the fourth frequency converter 280, respectively. The second local oscillator signal output to the second frequency converter 272 is used for frequency conversion of the two interference signals HV and VV in the second frequency converter 272, as described above.

[0090] Next, the interference signals HH, VH, HV, and VV output from power splitter 270 to high-pass filter 277 will be described. High-pass filter 277 attenuates signals with frequencies lower than frequency f1. Of the four interference signals HH, VH, HV, and VV, high-pass filter 277 passes three interference signals VH, HV, and VV (see FIG. 2) that have frequencies equal to or higher than frequency f1, and outputs them to third frequency converter 278.

[0091] The first local oscillator signal split by the power splitter 268 is further output to the third frequency converter 278. The third frequency converter 278 generates signals at the sum frequency and difference frequency between the three input interference signals VH, HV, and VV and the first local oscillator signal. The frequency of the first local oscillator signal is frequency f1. Therefore, the three interference signals VH, HV, and VV are converted into signals that are up-converted by frequency f1 and signals that are down-converted by frequency f1.

[0092] The third frequency converter 278 outputs the generated signal to the high-pass filter 279. The high-pass filter 279 attenuates signals with frequencies lower than frequency f2. Because the interference signals VH, HV, and VV have frequencies higher than frequency f1 (see FIG. 2), the signals obtained by up-converting the interference signals VH, HV, and VV by frequency f1 also have frequencies higher than frequency f2. Therefore, the high-pass filter 279 passes the signals obtained by up-converting the interference signals VH, HV, and VV by frequency f1. On the other hand, the signals obtained by down-converting the interference signals VH, HV, and VV by frequency f1 are converted so that the frequency f1 in FIG. 2 becomes DC (i.e., 0). For this reason, high-pass filter 279 attenuates the signals obtained by down-converting interference signals VH, HV, and VV by frequency f1, that is, the signals obtained by down-converting interference signals VH, HV, and VV having frequencies lower than frequency f2 by frequency f1, and passes only the signal obtained by down-converting interference signal VV having a frequency equal to or higher than frequency f2 by frequency f1. Therefore, high-pass filter 279 passes the signals obtained by up-converting interference signals VH, HV, and VV by frequency f1 and the signal obtained by down-converting interference signal VV by frequency f1, and outputs them to fourth frequency converter 280.

[0093] The second local oscillator signal split by the power splitter 274 is also output to the fourth frequency converter 280. The fourth frequency converter 280 generates signals at the sum frequency and difference frequency between the second local oscillator signal and the signals obtained by up-converting the input interference signals VH, HV, and VV by frequency f1 and the signals obtained by down-converting the interference signal VV by frequency f1. The frequency of the second local oscillator signal is frequency f2. Therefore, the signals obtained by up-converting the interference signals VH, HV, and VV by frequency f1 and the signals obtained by down-converting the interference signal VV by frequency f1 are converted into signals up-converted by frequency f2 and signals down-converted by frequency f2. In detail, the fourth frequency converter 280 converts the interference signals VH, HV, and VV by frequency f1 into signals obtained by further up-converting them by frequency f2 (signals obtained by up-converting the interference signals VH, HV, and VV by frequency f1+f2), and converts the interference signals VH, HV, and VV by frequency f1 into signals obtained by further down-converting them by frequency f2 (signals obtained by converting the interference signals VH, HV, and VV by frequency f1-f2, i.e., The following signals are generated: a signal obtained by down-converting the interference signal VV by frequency f1 and then further up-converting it by frequency f2 (a signal obtained by converting the interference signal VV by frequency f2-f1, i.e., a signal obtained by up-converting the interference signal VV by frequency f1); and a signal obtained by down-converting the interference signal VV by frequency f1 and then further down-converting it by frequency f2 (a signal obtained by down-converting the interference signal VV by frequency f1+f2).

[0094] The fourth frequency converter 280 outputs the generated signal to the low-pass filter 281. The low-pass filter 281 converts the frequency f k / 2. The signals obtained by up-converting the interference signals VH, HV, and VV by the frequency f1+f2, the signals obtained by down-converting the interference signals VH, HV, and VV by the frequency f1, and the signals obtained by up-converting the interference signal VV by the frequency f1 are attenuated at the frequency f k / 2 (see FIG. 2), all of the signal is attenuated. On the other hand, the signal obtained by down-converting the interference signal VV by the frequency f1+f2 is converted so that the frequency f1+f2 in FIG. 2 becomes DC (i.e., 0). Therefore, the low-pass filter 78 passes only the signal obtained by down-converting the interference signal VV by the frequency f1+f2, and outputs it to channel D of the second data acquisition unit 75.

[0095] From the above, even if the interference signals HH, VH, HV, and VV are processed using the signal processing unit 260 shown in Figure 6, the four interference signals HH, VH, HV, and VV can each be downconverted to the same frequency band, and the first data acquisition unit 64 and the second data acquisition unit 75 can acquire the four interference signals HH, VH, HV, and VV in the same frequency band.

[0096] Furthermore, signal filtering is easier in the signal processing unit 60 shown in Fig. 4 and the signal processing unit 260 shown in Fig. 6. Furthermore, the signal processing unit 60 shown in Fig. 4 uses three frequency converters 66, 71, and 77, while the signal processing unit 260 shown in Fig. 5 uses four frequency converters 166, 172, 178, and 179, and the signal processing unit 260 shown in Fig. 6 also uses four frequency converters 266, 272, 278, and 280. Therefore, the signal processing unit 60 shown in Fig. 4 can reduce the number of frequency converters.

[0097] Example 2 In the first embodiment, the interference signal is detected by one balance detector 58, but the present invention is not limited to such a configuration. For example, as shown in Fig. 7, the interference signal may be detected by using two balance detectors 149 and 152.

[0098] The optical tomographic imaging apparatus 2 of this embodiment includes a light source 11, SMFCs 12 and 13, a measuring light generation unit 14, a reference light generation unit 140, a polarized receiver 142, an observation optical system 80, a K clock signal generation unit 82, an alignment optical system (not shown), a signal processing unit 360 (see FIG. 9), and a calculation unit 90 (see FIG. 3). Note that the light source 11, SMFCs 12 and 13, and measuring light generation unit 14 have substantially the same configurations as the light source 11, SMFCs 12 and 13, and measuring light generation unit 14 of the first embodiment, and therefore detailed description thereof will be omitted.

[0099] In this embodiment as well, the measurement light generation unit 14 includes a first polarization-dependent delay line 16. Therefore, the SMFC 24 receives horizontally polarized reflected light (light obtained by reflecting the horizontally polarized measurement light from the eye 100), vertically polarized reflected light (light obtained by reflecting the vertically polarized measurement light from the eye 100), and calibration light containing horizontally and vertically polarized components. For ease of explanation, detailed description of the calibration light will be omitted below. The horizontally polarized reflected light and vertically polarized reflected light input to the SMFC 24 pass through the SMF and are output to the polarization receiver 142.

[0100] The reference light generating unit 140 will now be described. The reference light generating unit 140 includes a reference variable delay line 51 and a polarization control device 141. The reference light output from the SMFC 13 passes through an SMF and is input to the reference variable delay line 51. Note that the reference variable delay line 51 has substantially the same configuration as the reference variable delay line 51 of the first embodiment, and therefore a detailed description thereof will be omitted. The reference light generating unit 140 of this embodiment differs from the reference light generating unit 40 of the first embodiment in that it does not include a polarization-dependent delay line. The reference light output from the reference variable delay line 51 passes through an SMF and is output to a polarization receiver 142 via the polarization control device 141.

[0101] The polarized light receiver 142 includes collimator lenses 143 and 145, a beam splitter 144, a linear polarizer 146, polarized beam splitters 147 and 153, lenses 148, 151, 154 and 156, a first balanced detector 149, mirrors 150 and 155, and a second balanced detector 152.

[0102] The polarization receiver 142 receives the horizontally polarized reflected light and the vertically polarized reflected light from the SMFC 24 , and also receives the reference light from the reference variable delay line 51 via the polarization control device 141 .

[0103] The horizontally polarized reflected light and vertically polarized reflected light output from the SMFC 24 to the polarization receiver 142 are emitted to a collimator lens 143 and then emitted from the collimator lens 143 to a beam splitter 144 .

[0104] Furthermore, the reference light output from reference variable delay line 51 to polarization receiver 142 via polarization control device 141 is emitted to collimator lens 145. The reference light emitted to collimator lens 145 is emitted to beam splitter 144 via linear polarizer 146. Linear polarizer 146 splits the reference light into a horizontally polarized component (hereinafter also referred to as horizontally polarized reference light) and a horizontally polarized component (hereinafter also referred to as vertically polarized reference light). Therefore, horizontally polarized reference light and vertically polarized reference light are emitted to beam splitter 144.

[0105] Beam splitter 144 splits the emitted light (horizontally polarized reflected light, vertically polarized reflected light, horizontally polarized reference light, and vertically polarized reference light), and outputs the split light to polarizing beam splitters 147 and 153, respectively.

[0106] First, the light output from beam splitter 144 to polarizing beam splitter 147 will be described. Polarizing beam splitter 147 transmits the horizontally polarized component and reflects the vertically polarized component. Polarizing beam splitter 147 transmits the horizontally polarized component (more specifically, the horizontally polarized components of the horizontally polarized reflected light and the vertically polarized reflected light, and the horizontally polarized reference light) and outputs it to lens 148. The horizontally polarized component output to lens 148 is input to the SMF, passes through the SMF, and input to first balance detector 149.

[0107] Polarizing beam splitter 147 also reflects the vertically polarized component (more specifically, the vertically polarized component of the horizontally polarized reflected light and the vertically polarized reflected light, and the vertically polarized reference light) and outputs it to mirror 150. The vertically polarized component output to mirror 150 is input to the SMF via lens 151, passes through the SMF and input to second balance detector 152.

[0108] Next, the light output from beam splitter 144 to polarizing beam splitter 153 will be described. Polarizing beam splitter 153 also transmits the horizontally polarized component and reflects the vertically polarized component. Polarizing beam splitter 153 transmits the horizontally polarized component (more specifically, the horizontally polarized components of the horizontally polarized reflected light and the vertically polarized reflected light, and the horizontally polarized reference light) and outputs it to lens 154. The horizontally polarized component output to lens 154 is input to the SMF, passes through the SMF, and input to first balance detector 149.

[0109] Polarizing beam splitter 153 also reflects the vertically polarized component (more specifically, the vertically polarized component of the horizontally polarized reflected light and the vertically polarized reflected light, and the vertically polarized reference light) and outputs it to mirror 155. The vertically polarized component output to mirror 155 is input to the SMF via lens 156, passes through the SMF and input to second balanced detector 152.

[0110] The first balance detector 149 and the second balance detector 152 perform differential amplification and noise reduction processing on the two input interference lights, convert them into electrical signals (interference signals), and output the interference signals to the signal processing unit 360 (see Figure 9).

[0111] The interference signal generated in this embodiment will be further described. In the polarization receiver 142, the horizontally polarized components (the horizontally polarized components of the horizontally polarized reflected light and the vertically polarized reflected light, and the horizontally polarized reference light) are input to the first balance detector 149. Therefore, in the first balance detector 149, interference light is generated when the horizontally polarized component of the horizontally polarized reflected light interferes with the horizontally polarized reference light, and this interference light is converted into an interference signal HH. Furthermore, interference light is generated when the horizontally polarized component of the vertically polarized reflected light interferes with the horizontally polarized reference light, and this interference light is converted into an interference signal VH. Furthermore, in the first polarization-dependent delay line 16, the optical path length of the horizontally polarized measurement light is made shorter than the optical path length of the vertically polarized measurement light. Therefore, as shown in FIG. 8( a), with respect to the interference signals HH and VH, the interference signal HH obtained by converting the interference light generated from the horizontally polarized reflected light is detected at a shallower position than the interference signal VH obtained by converting the interference light generated from the vertically polarized reflected light.

[0112] Furthermore, in the polarization receiver 142, the vertically polarized components (the vertically polarized components of the horizontally polarized reflected light and the vertically polarized reflected light, and the vertically polarized reference light) are input to the second balance detector 152. Therefore, in the second balance detector 152, interference light is generated when the vertically polarized component of the horizontally polarized reflected light interferes with the vertically polarized reference light, and this interference light is converted into an interference signal HV. Furthermore, interference light is generated when the vertically polarized component of the vertically polarized reflected light interferes with the vertically polarized reference light, and this interference light is converted into an interference signal VV. Furthermore, since the optical path length of the horizontally polarized measurement light is shorter than the optical path length of the vertically polarized measurement light, as shown in FIG. 8( b), with respect to the interference signals HV and VV, the interference signal HV obtained by converting the interference light generated from the horizontally polarized reflected light is detected at a shallower position than the interference signal VV obtained by converting the interference light generated from the vertically polarized reflected light. Note that, in this embodiment as well, the Nyquist frequency is the frequency f1+f k / 2.

[0113] Next, the processing of interference signals HH, VH, HV, and VV in signal processing unit 360 will be described with reference to Fig. 9. First, the interference signals HH and VH output from first balance detector 149 to signal processing unit 360 will be described. As shown in Fig. 9, the interference signals HH and VH output from first balance detector 149 to signal processing unit 360 are split by power splitter 361 and output to low-pass filter 362 and high-pass filter 363, respectively.

[0114] The low-pass filter 362 filters out the interference signals HH and VH at a frequency f k Only the interference signal HH (see FIG. 8) having a frequency equal to or lower than 1 / 2 is passed through and output to channel A of the first data acquisition unit 64.

[0115] Next, the interference signals HH and VH output from the power splitter 361 to the high-pass filter 363 will be described. The high-pass filter 363 passes only the interference signal VH (see FIG. 8), which has a frequency equal to or higher than frequency f1, out of the interference signals HH and VH, and outputs it to the first frequency converter 365. A first local oscillator signal is also output to the first frequency converter 365, as will be described later. The first frequency converter 365 up-converts and down-converts the interference signal VH by frequency f1, which is the frequency of the first local oscillator signal, and outputs it to the low-pass filter 367. The low-pass filter 367 up-converts and down-converts the interference signal VH up-converted by frequency f1 and the interference signal VH down-converted by frequency f1, out of the interference signal VH up-converted by frequency f1 and the interference signal VH down-converted by frequency f1. k The first data acquisition unit 64 passes only the interference signal VH (see FIG. 8) down-converted by frequency f1, which is a frequency equal to or lower than 1 / 2, and outputs the signal to channel B of the first data acquisition unit 64.

[0116] Here, the path of the first local oscillator signal input to first frequency converter 365 will be described. The first local oscillator signal output from first local oscillator 39 to signal processing unit 360 is split by power splitter 366 and output to first frequency converter 365 and second frequency converter 371, respectively. The first local oscillator signal output to first frequency converter 365 is used for frequency conversion of interference signal VH in first frequency converter 365, as described above.

[0117] Next, a description will be given of the interference signals HV, VV output from the second balance detector 152 to the signal processing unit 360. The interference signals HV, VV output from the second balance detector 152 to the signal processing unit 360 are split by a power splitter 368 and output to a low-pass filter 369 and a high-pass filter 370, respectively.

[0118] The low-pass filter 369 filters out the interference signals HV and VV at a frequency f k Only the interference signal HV (see FIG. 8) having a frequency equal to or lower than 1 / 2 is passed through and output to channel D of the second data acquisition unit 75.

[0119] Next, the interference signals HV, VV output from the power splitter 368 to the high-pass filter 370 will be described. The high-pass filter 370 passes only the interference signal VV (see FIG. 8) of the interference signals HV, VV, which has a frequency equal to or higher than frequency f1, and outputs it to the second frequency converter 371. The first local oscillator signal split by the power splitter 366 is also output to the second frequency converter 371. The second frequency converter 371 up-converts and down-converts the interference signal VV by frequency f1, which is the frequency of the first local oscillator signal, and outputs it to the low-pass filter 372. The low-pass filter 372 up-converts and down-converts the interference signal VV by frequency f1, which is the frequency of the first local oscillator signal, and outputs it to the low-pass filter 372. The low-pass filter 372 filters out the interference signal VV up-converted by frequency f1 and the interference signal VV down-converted by frequency f1. k Only the interference signal VV (see FIG. 8) down-converted by frequency f1, which is a frequency not higher than 1 / 2, passes through and is output to channel C of the second data acquisition unit 75.

[0120] In this embodiment, four interference signals HH, VH, HV, and VV are acquired using two balanced detectors 149 and 152. Even when two balanced detectors 149 and 152 are used, the signal processing unit 360 down-converts the four interference signals HH, VH, HV, and VV so that they have the same frequency band, allowing the first data acquisition unit 64 and the second data acquisition unit 75 to acquire the four interference signals HH, VH, HV, and VV in the same frequency band. Furthermore, because the four interference signals HH, VH, HV, and VV can be detected in the same frequency band (i.e., a frequency band smaller than the Nyquist frequency), the detection sensitivity of the four interference signals HH, VH, HV, and VV can be increased.

[0121] Although the optical tomographic imaging apparatus 1 of the first embodiment and the optical tomographic imaging apparatus 2 of the second embodiment are configured to measure the subject's eye 100, they are not limited to such a configuration. The configurations of the first and second embodiments can also be applied to optical tomographic imaging apparatuses that measure objects other than the subject's eye 100.

[0122] Furthermore, while the polarization-sensitive optical tomographic imaging apparatuses 1 and 2 are used in the above-described first and second embodiments, the present invention is not limited to such a configuration. For example, even in an optical tomographic imaging apparatus that is not polarization-sensitive, the interference signal may be down-converted in the signal processing unit and the down-converted interference signal may be input to the data acquisition unit. By down-converting the interference signal, even in a case where the optical system is configured so that the interference signal is detected away from DC, the interference signal can be down-converted to near DC and input to the data acquisition unit.

[0123] The following describes points to note regarding the optical tomographic imaging apparatuses 1 and 2 described in the embodiments. The SMFC 57, the first balance detector 149, and the second balance detector 152 in the embodiments are examples of an "interference light generation unit," the balance detector 58, the first balance detector 149, and the second balance detector 152 are examples of an "interference light detection unit," the signal processing units 60, 160, 260, and 360 are examples of a "demultiplexer unit," and the first frequency converters 66, 166, 266, and 365, the second frequency converters 71, 172, 272, and 371, the third frequency converters 77, 178, and 278, and the fourth frequency converter 280 are examples of a "down-conversion unit."

[0124] Although specific examples of the technology disclosed in this specification have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. Furthermore, the technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings simultaneously achieves multiple objectives, and achieving one of those objectives itself has technical utility. [Explanation of symbols]

[0125] 1, 2: Optical tomography imaging device 11:Light source 14: Measurement light generation section 16: First polarization dependent delay line 18, 44: Linear polarizer 19, 45, 147, 153: Polarizing beam splitter 26: Measuring arm 39: 1st local oscillator 40:Reference light generation section 42: Second polarization dependent delay line 51: Reference variable delay line 56: Second local oscillator 57:SMFC 58: Balance detector 60: Signal processing section 64: First data acquisition unit 66, 166, 266, 365: First frequency converter 71, 172, 272, 371: Second frequency converter 75: Second data acquisition unit 77, 178, 278: Third frequency converter 80: Observation optical system 82: K clock signal generation unit 90: Arithmetic section 142: Polarized receiver 144: Beam splitter 149: First balance detector 152: Second balance detector 179, 280: 4th frequency converter

Claims

1. a wavelength swept light source; a measurement light generating unit that irradiates the object with light from the light source and generates reflected light from the object; a reference light generating unit that guides light from the light source and generates reference light; an interference light generating unit that generates at least two interference lights by combining the reflected light generated by the measurement light generating unit and the reference light generated by the reference light generating unit; an interference light detection unit that outputs at least two interference signals from the at least two interference lights generated by the interference light generation unit; a demultiplexer unit that converts the frequency of at least one of the at least two interference signals output from the interference light detection unit; a data acquisition unit that digitizes the electrical signal output from the demultiplexer unit to acquire data; a computing device that generates tomographic information of the object from the data acquired by the data acquisition unit, the demultiplexer unit includes a down-conversion unit that electrically down-converts at least one of the at least two interference signals output from the interference light detection unit, the data acquisition unit is configured to separately acquire data of the electrical signals that have passed through at least two different paths in the demultiplexer unit; The arithmetic unit performs spectral analysis on the interference signal acquired by the data acquisition unit to generate tomographic information of the object.

2. The measurement light generation unit generating a first polarization measurement light oscillating in a first direction from light of the light source and a second polarization measurement light oscillating in a second direction different from the first direction and having an optical path length different from that of the first polarization measurement light, and irradiating the first polarization measurement light and the second polarization measurement light onto the object; generating a first polarized reflected light oscillating in the first direction and a second polarized reflected light oscillating in the second direction from the first polarized measurement light reflected from the object; generating third polarized reflected light oscillating in the first direction and fourth polarized reflected light oscillating in the second direction from the second polarized measurement light reflected from the object; the interference light detection unit detects first interference light obtained by combining the first polarized reflected light and the reference light, second interference light obtained by combining the second polarized reflected light and the reference light, third interference light obtained by combining the third polarized reflected light and the reference light, and fourth interference light obtained by combining the fourth polarized reflected light and the reference light, The optical tomographic imaging apparatus according to claim 1 , wherein the down-conversion unit down-converts an interference signal generated from the third interference light and the fourth interference light.

3. the reference light generating unit generates a first reference light and a second reference light having an optical path length different from that of the first reference light; The interference light detection unit combining the first polarized reflected light and the first reference light and detecting the first interference light; combining the second polarized reflected light with the second reference light and detecting the second interference light; combining the third polarized reflected light with the first reference light and detecting the third interference light; combining the fourth polarized reflected light with the second reference light and detecting the fourth interference light; The optical tomographic imaging apparatus according to claim 2 , wherein the down-conversion unit down-converts an interference signal generated from the second interference light, the third interference light, and the fourth interference light.

4. at least one of the measurement light generating unit and the reference light generating unit includes a local oscillator that optically generates a signal for frequency conversion; 2. The optical tomographic imaging apparatus according to claim 1, wherein the demultiplexer section down-converts the interference signal output from the interference light detection section using a signal generated by the local oscillator.

5. at least one of the measurement light generating unit and the reference light generating unit includes a local oscillator that optically generates a signal for frequency conversion; the demultiplexer unit further includes a high-pass filter; the high-pass filter is configured to attenuate at least one interference signal having a small frequency among four interference signals generated from the first interference light, the second interference light, the third interference light, and the fourth interference light; 4. The optical tomographic imaging apparatus according to claim 2, wherein the down-conversion unit down-converts the interference signal that has passed through the high-pass filter, using a signal generated by the local oscillator.

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